JP2020520410A - How to connect components by means of metal paste - Google Patents

Abstract

The present invention comprises (1) applying a metal paste containing an organic solvent to the contact surface of the first component, and (2) applying the metal to the contact surface of a second component connected to the first component. Optionally applying a paste; (3) creating a sandwich structure having the two components and a layer of metal paste between them; (4) the layer of the metal paste between the two components. And (5) pressureless sintering the sandwich structure comprising the layer of dried metal paste, the method comprising the steps of: Pressure sintering relates to a method of connecting components, which is performed by radiation with IR radiation having a peak wavelength in the wavelength range between 750 and 1500 nm. The component is selected from the group consisting of a substrate, an active component and a passive component. One or both of the components are transparent to the IR radiation. Steps (4) and (5) are performed under an oxygen atmosphere or an oxygen-free atmosphere. In both cases, at least one of the components has an oxygen sensitive contact surface.

Description

The invention relates to a method of connecting components by means of a metal paste. In the fields of power and consumer electronics, the connection of components with high pressure and temperature sensitivity represents a particular challenge. For this reason, such pressure and temperature sensitive components are often connected to each other by adhesion. However, the bonding technique has the disadvantage that the contacts between the components, which each have only one poor thermal or electrical conductivity, are made by the bonding technique.

A well-known solution to this problem is to connect the components to be connected in a pressure-free manner by sintering. Pressureless sintering represents a very simple way to connect components in a stable manner.

The metal paste containing the organic solvent is therefore usually provided on one or both contacting surfaces to be connected of the components to be connected, the contacting surfaces being connected by forming a sandwich arrangement thereof. The layers of metal paste located therein are in contact with each other. Thereby, the two contact surfaces of the component facing each other form a joint overlap surface. The drying step is followed by an increased temperature and then a sintering step, the sintering step being carried out at a further increased temperature in a pressure-free manner (without pressing), in the process of A fixed mechanical connection of is created. Drying and sintering are usually done in a convection oven. Depending on the size of the respective connection or contact surface or overlapping surface of the components to be connected in the range of 1 to 25 mm ² , this prior art drying process can be carried out at oven temperatures between 100° C. and 160° C., It requires a time in the range of 30 to 180 minutes. Choosing a drying period that is too short often results in the formation of unwanted imperfections such as shrinkage cavities in the layer that are still sintering. Such pores and imperfections may not only mechanically weaken subsequent connections in the form of subsequently sintered layers, but also their electrical and thermal conductivity. There is.

The invention consists in carrying out drying as well as pressureless sintering by IR radiation (infrared radiation) rather than by convection. The method according to the invention comprises: (1) applying a metal paste containing an organic solvent to the contact surface of a first component; and (2) applying to the contact surface of a second component connected to the first component. Optionally applying the metal paste; (3) manufacturing a sandwich structure with the two components and a layer of the metal paste in between; (4) the metal paste between the two components. A method of sintering a component comprising the steps of: drying a layer; and (5) pressurelessly sintering the sandwich structure comprising a layer of dried metal paste, the method comprising the steps of: Pressure sintering is a method of connecting components, characterized in that it is performed by IR radiation (infrared radiation) having a peak wavelength in the wavelength range between 750 and 1500 nm. The method according to the invention comprises steps (1) to (5). They are specific consecutive steps, in particular directly consecutive steps without intermediate steps.

As part of this invention, the term component preferably comprises individual parts. These individual parts desirably cannot be divided into smaller parts. Each component has one and optionally multiple contact surfaces. The contact surface is generally metallic, for example in the form of a metallization layer. The metal of the component or contact surface can be a pure metal or an alloy of metals. Aluminum, copper, silver, gold, nickel, palladium, iron, and platinum are examples of metals.

The contact surfaces of the components used in the method according to the invention are, for example, in the range between 1 and 150 mm ² , in particular between >20 and 150 mm ² , in particular between 40 and 150 mm ^2. Is. The method according to the invention also does not have to accept the formation of defects of the type described above, and can nevertheless be carried out on components with large contact surfaces with a very short drying and pressureless sintering. .. The connected first and second components may be of the same type, ie they may be substrates in both cases, for example, or they may each be a plurality of active or passive components. Or one active and passive component. However, one component can be a substrate and the other component can be an active or passive component, and vice versa. Substrates, active components and passive components are, inter alia, parts used in electronics.

ＩＭＳ基板（絶縁金属基板）、ＤＣＢ基板（直接銅接合基板）、ＡＭＢ基板（活性金属ろう付け基板）、セラミック基板、ＰＣＢ（印刷回路基板）、およびリードフレームは、基板の例である。ダイオード、ＬＥＤ（発光ダイオード）、ダイ（半導体チップ）、ＩＧＢＴ（絶縁ゲートバイポーラトランジスタ）、ＩＣ（集積回路）、およびＭＯＳＦＥＴ（金属酸化物半導体電界効果トランジスタ）は、能動コンポーネントの例である。センサー、ベースプレート、冷却エレメント、抵抗、キャパシタ、およびコイルは、受動コンポーネントの例である。有機溶剤を含む金属ペーストは、この発明に従う方法のステップ（１）で第１のコンポーネントの接触面に塗布される。 Therefore, the following embodiments can be different, for example.

IMS substrates (insulating metal substrates), DCB substrates (direct copper bonded substrates), AMB substrates (active metal brazed substrates), ceramic substrates, PCBs (printed circuit boards), and leadframes are examples of substrates. Diodes, LEDs (light emitting diodes), dies (semiconductor chips), IGBTs (insulated gate bipolar transistors), ICs (integrated circuits), and MOSFETs (metal oxide semiconductor field effect transistors) are examples of active components. Sensors, base plates, cooling elements, resistors, capacitors, and coils are examples of passive components. A metal paste containing an organic solvent is applied to the contact surface of the first component in step (1) of the method according to the invention.

Metal pastes containing organic solvents are also common metal plates, also known as metal sinter pastes, known to those skilled in the art as a means of creating sinter connections between components or contact surfaces of components, respectively. Such a metal paste contains, for example, 25% to 90% by weight of sinterable metal particles, in particular silver particles, silver alloy particles, copper particles and/or copper alloy particles, and 5% to 30% of an organic solvent. % By weight, particularly 0% to 65% by weight of metal precursor compound (metal precursor), especially silver oxide, silver carbonate, and 0% to 5% of sintering aids such as peroxides and formates. %, and other additives such as saturated fatty acids and/or polymers such as ethyl cellulose or polyimide from 0% to 5% by weight.

Such metal pastes are disclosed in various embodiments, for example WO2016/071005A1, EP3009211A1, WO2016/028221A1, WO2015, 193014A1, WO20141776445A1, WO2014/170050A1, WO2011/0266224A1, WO2011/026623A1, EP2577282A15, EP2572814A1 and EP2572814A1, EP2572829A1. Has been done.

The application of the metal paste to the contact surface of the first component can be carried out by a common method, for example, a printing method such as screen printing, stencil printing, or spraying. On the other hand, the application of the metal paste can also be performed by a dispensing technology, a pin transfer, or a dipping. The method according to the invention comprises an optional step (2). When step (2) occurs, the metal paste already indicated above is also applied to the contact surface of the second component. The coating method described above is a possible coating method.

A sandwich structure with two components and a metal paste between the two components is created in step (3). For this purpose, a first component with a contact surface with metal paste is optionally attached to the contact surface of a second component with metal paste, or the second component is optionally equipped with a metal pace. The contact surface of the first component with the metal paste. As a result, a layer of metal paste is between the components to be connected.

The wet film thickness of the metal paste layer is preferably in the range of 20 to 200 μm. Here, the thickness of the wet film is understood as the distance between the contact surfaces of the components before drying, which face each other or are arranged facing each other. The wet film layer can depend, for example, on the selected method of applying the metal paste. In the case of the metal paste applied by the screen printing method, the thickness of the wet film is, for example, in the range of 20 to 50 μm, in the case of stencil printing, it is in the range of 50 to 200 μm, and in the case of the dispense application, for example, 20 to 100 μm. In the case of coating by spraying, it may be, for example, in the range of 20 to 70 μm.

In step (4) of the method according to the invention, the layer of metal paste between the contact surfaces of the two components is dried. In response to drying, the organic solvent is removed from the metal paste. According to a preferred embodiment, the organic solvent part of the dried metal paste is based on the original part of the organic solvent of the metal paste, i.e. application-ready metal paste, for example 0-5. %, or between 0 and <1% weight. In other words, 95-100% by weight or >99-100% by weight of the organic solvent or solvents originally contained in the metal paste are removed, for example, upon drying according to this preferred embodiment. ..

Drying is carried out by irradiation with IR radiation having a peak wavelength in the wavelength range of 750 to 1500 nm, preferably 750 to 1200 nm. If desired, simultaneous support can be provided by convection, but this is neither necessary nor preferred. In other words, it is preferable and not only possible to carry out the drying only by irradiating with IR radiation having a peak wavelength in the wavelength range of 750 to 1500 nm, preferably 750 to 1200 nm.

Examples of radiation sources that can be used for such IR radiation include the common NIR radiators (near infrared radiators). Such NIR emitters are available, for example, from Heraeus. The NIR radiator can be, for example, a high performance short wave radiator. The radiator or the individual NIR radiators can be operated with a power output in the range of, for example, 15 to 100 w/cm (watts per cm length of the radiator), preferably 20 to 50 w/cm. Thereby, the emitter surface temperature (spiral filament temperature) of the NIR emitter is, for example, in the range of 1800 to 3000°C, preferably in the range of 1850 to 2500°C. Suitable NIR emitters have, for example, an emission spectrum with a maximum in the range 750 to 1500 nm, preferably 750 to 1200 nm, especially 750 to 1500 nm, or 750 to 1200 nm.

The IR radiation can be carried out statically or in a pass-through plant, whereby a sandwich structure illuminated with components and a metal paste dried in between, and/or an IR radiation source or Multiple radiation sources move relative to each other. One or both of the components are transparent to IR radiation, i.e. partially or completely transparent and in each case sufficiently transparent for the purposes of the method according to the invention. In other words, at least one of the components does not completely absorb IR radiation. The IR radiation is provided through one or both of the components that are transparent to the IR radiation. It is preferred if the IR irradiation is carried out via only one or one component which is transparent to the IR radiation. IR irradiation is preferably done from above through the components on top. Substrates such as ceramic substrates, active components such as diodes, LEDs, dies, IGBTs, ICs, MOSFETs, passive components such as sensors, ceramic cooling elements, resistors, capacitors and coils are examples of components and It is transparent.

The distance between the IR radiation sources, and more precisely between the radiation discharge surface of the IR radiation source and the layer of the metal paste to be pressureless sintered is for example in the range 1 to 50 cm, preferably 5 Between 20 and 20 cm. The facing contact surfaces of the two components form a joint overlap surface with each other. Thereby the contact surface of the component including the smaller contact surface is generally fully utilized, ie the size of the overlapping surface generally corresponds to the size of the complete contact surface of the component including the smaller contact surface.

Depending on the size of the joint overlapping surfaces formed from the facing surfaces of the two components, for example in the range from 1 to 150 mm ^2, the drying process, which is only affected by IR in particular, is for example from 1 to 60 minutes. It only requires a range of times and is therefore significantly shorter than in the case of the oven drying described above according to the prior art. There are no quality drawbacks compared to oven drying. For small overlapping surfaces at the lower end of the range, a short drying period is sufficient, and for large overlapping surfaces, the drying period is at the upper end of the range. The person skilled in the art can select the IR irradiation parameters and/or the drying period of step (4) so that sintering or pre-sintering of the dry or dry metal paste can be avoided.

The sandwich structure comprising a layer of dry metal paste is pressureless sintered in step (5) of the method according to the invention. As in the case of drying according to step (4), pressureless sintering is also carried out by irradiation with the IR radiation. Thereby, steps (4) and (5) are advantageously such that the IR irradiation is continued without interruption for the purpose of step (5), eg after completion of the drying according to step (4). In this way, they can advantageously continue each other. Therefore, steps (4) and (5) melt substantially together. However, it is also possible to carry out step (4) and step (5) and interrupt the cooldown during and in between.

Pressureless sintering is carried out by irradiating with IR radiation having a peak wavelength in the wavelength range of 750 to 1500 nm, preferably 750 to 1200 nm. If desired, convection can provide simultaneous support, but this is neither necessary nor recommended. In other words, it is only possible to carry out pressureless sintering only by irradiating with IR radiation having a peak wavelength in the wavelength range of 750 to 1500 nm, preferably 750 to 1200 nm, as in the case of drying. Not preferred. Regarding the radiation source for IR radiation and its operating condition, reference is made to what has been said above in connection with the drying step (4).

As in the drying step (4), IR irradiation can be carried out in static or pass-through plants. This causes the components and the sandwich structure and/or the IR radiation source illuminated by the metal paste which is pressurelessly sintered between them to move relative to each other. As in the drying step (4), IR irradiation is performed through one or both components that are transparent to IR radiation. It is preferred if the IR irradiation is carried out via only one or one component that is transparent to the IR irradiation. IR irradiation is preferably done from above through the components on top.

The distance between the IR radiation sources, or more precisely the distance between the radiation discharge surface of the IR radiation source and the layer of metal paste to be sintered without pressure, is for example in the range 1 to 50 cm, preferably It is between 5 and 20 cm. For example, pressureless sintering by IR irradiation may take, for example, 15 minutes to 90 minutes, depending on the size of the joining overlap surface formed from the contacting surfaces of two components in the range of 1 to 150 mm ² . It only needs a time period in between. There are no quality drawbacks compared to pressureless sintering in the oven. In the case of a small overlapping surface at the lower end of the above range, a short drying period is sufficient for pressureless sintering, and in the case of a large overlapping surface, the drying period is at the upper end of the above range.

Steps (4) and (5) can be carried out in an atmosphere without particular restrictions. Therefore, drying and pressureless sintering can be carried out in an atmosphere containing oxygen, for example air. Even in the case of components containing contact surfaces that are essentially oxidation-sensitive, for example copper or nickel contact surfaces, the possible relatively short drying times and also pressure-free baking that are possible as a result of the method according to the invention are possible. As a result of the short binding time, it is possible to carry out the operation in an oxygen atmosphere, for example air.

It goes without saying that, if necessary, it is possible to perform drying and pressureless sintering in an oxygen-free atmosphere. As part of the present invention, an oxygen-free atmosphere should be understood to be an atmosphere whose oxygen content is 100 ppm volume or less (volume ppm), preferably 10 ppm or less, even more preferably 1 ppm vol or less. ..

In summary, the method according to the invention for connecting the components provides a greater drying time and lossless sintering period compared to the prior art operating in convection, a pressureless sinter-bonding technique which is of great advantage. Extended application to components with contact surfaces, quality, increased applicability to parts with large contact surfaces, and even when working with parts containing oxidation-sensitive contact surfaces, e.g. copper or nickel contact surfaces. It should be noted that it has advantages such as no need for activation.

Example:
Reference Example 1, production of metal paste : 85 parts by weight of silver particles (containing 0.6% by weight of lauric acid/stearic acid in a coated silver flake with a weight ratio of 25:75), A metal paste was formed by mixing 7.4 parts by weight of α-terpineol, 7.4 parts by weight of iso-tridecanol and 0.2 parts by weight of ethyl cellulose.

Application of the metal paste of Reference Example 2, Example 1 and formation of a sandwich arrangement : The metal paste from Example 1 was stencil-printed over the entire surface of a DCB substrate including a surface of 75 μm and a surface of 4 mm-4 mm. Was applied to. Silicon chips containing a 4 mm-4 mm silver contact surface were attached to the paste thus coated by forming a sandwich structure containing the bonding overlap surface of the DCB substrate and the 4 mm-4 mm chips.

Oven dried sandwich structure from Reference Example 3a, Example 2 : The sandwich structure made according to Example 2 has a residual solvent content of less than 0.5% by weight, based on the organic solvent originally contained in the metal paste. Except for the above, it was dried under an atmosphere of nitrogen at an oven temperature of 150° C. (weight measurement). The drying process required 60 minutes.

Reference Example 3b, drying the sandwich structure of Example 2 under IR irradiation : a sandwich structure made according to Example 2 was used with a length of 30 cm, an output of 30 W/cm, a filament temperature of 2009° C. and a peak wavelength of 1100 nm NIR emitter. Was irradiated in the air from a distance of 10 cm from above the silicon chip, and based on the organic solvent originally contained in the metal paste (determined by gravimetric measurement), a residual solvent content of <0.5% by weight was obtained. Removed, the organic solvent was removed.
The drying process carried out by IR radiation alone requires 10 minutes.

Comparative Example 4a, Pressureless Sintering of Sandwich Structure Dried According to Example 3a in Oven : Sandwich structure made according to Example 3a is heated in a convection oven under nitrogen atmosphere at an oven temperature of 230° C. for 60 minutes. Sintered without pressure. After cooling, the adhesive strength was measured by shear strength. Thereby, the silicon chip was sheared by a shearing chisel at 260° C. at a rate of 0.3 mm/s. The force was recorded by a measuring box (DAGE, German device DAGE2000). Shear strengths above 20 N/mm ² have shown satisfactory results. Measured shear strength: 23 N/mm ² .

Comparative Example 4b, Pressureless Sintering of Sandwich Structure Dried According to Example 3b in Oven : Sandwich structure dried according to Example 3b in oven at 230° C. for 60 minutes in a convection oven under nitrogen atmosphere. Sintered without pressure. Then, as in Example 4a, the adhesive strength was determined by shear strength. Measured shear strength: 24 N/mm ² .

Example 4c according to the invention, pressureless sintering of a sandwich structure dried according to Example 3b under IR irradiation : the sandwich structure dried according to Example 3b has a length of 30 cm from the silicon chip at a distance of 10 cm, At a power of 30 W/cm, a filament temperature of 200° C., and a peak wavelength of 1100 nm, emitted for 20 minutes with an NIR emitter and pressureless sintered, the IR emission process from Example 3b being uninterrupted. Continue to. Therefore, adhesion is determined via shear strength as in Example 4a. Measured shear strength: 21 N/mm ² .

Application of the metal paste from Reference Example 5, Example 1 and formation of a sandwich structure : The metal paste from Example 1 was applied to a surface of 5 mm-8 mm by stencil printing with a 75 μm a wet film layer. The included wet film layer was applied over the entire surface of the DCB substrate. Silicon chips containing 5 mm-8 mm silver contact surfaces were attached to pastes applied in this way by forming a sandwich structure containing the mating overlap surface of the DCB substrate and 5 mm-8 mm chips.

Reference Example 6a, Drying of Sandwich Structure from Example 5 in Oven : The sandwich structure made according to Example 5 is <0 based on the organic solvent originally contained in the metal paste (measured gravimetrically). It was dried at an oven temperature of 150° C. under a nitrogen atmosphere, except for residual solvent content of 0.5% by weight. The drying process required 90 minutes.

Reference Example 6b, Drying the sandwich structure from Example 5 under IR irradiation : The sandwich structure made according to Example 5 has a length of 30 cm, a power of 30 W/cm, a filament temperature of 2009°C and a peak of 1100 nm. Irradiation with a wavelength NIR emitter from above the silicon chip in air from a distance of 10 cm, whereby <0.5 wt% based on the solvent originally contained in the metal paste (measured gravimetrically). The organic solvent was removed, except for the residual solvent content of. The drying process performed by IR radiation alone required 20 minutes.

Comparative Example 7a, Pressureless Sintering of Sandwich Structure Dried According to Example 6a in an Oven : The sandwich structure made according to Example 6a has a convection oven under an atmosphere of nitrogen for 60 minutes at an oven temperature of 230°C. It was sintered without pressure inside. After cooling, adhesion was determined by shear strength. Thereby, the silicon chip was sheared by a shearing chisel at 260° C. at a rate of 0.3 mm/s. The force was recorded by a measuring box (DAGE, German device DAGE2000). Measured shear strength: 22 N/mm ² .

Comparative Example 7b, Pressureless Sintering of Sandwich Structure Dried According to Example 6b in an Oven : The sandwich structure made according to Example 6b has a convection oven in a nitrogen atmosphere for 60 minutes at an oven temperature of 230°C. It was sintered without pressure inside. Then, as in Example 7a, the adhesive strength was determined by shear strength. Measured shear strength: 22 N/mm ² .

Example 7c according to the invention, pressureless sintering of a dried sandwich structure according to Example 6b under IR radiation : the sandwich structure dried according to Example 6b has a length of 30 cm and an output of 30 w/cm, The filament temperature of 2009° C. and the peak wavelength of 1100 nm was emitted for 20 minutes at a distance of 10 cm with a NIR emitter from above the silicon chip and sintered without pressure, in this case the IR emission from Example 6b was: It continued without interruption. Therefore, adhesion was determined via shear strength, as in Example 7a. Measured shear strength: 23 N/mm ² .

Claims (14)

(1) applying a metal paste containing an organic solvent to the contact surface of the first component;
(2) optionally applying the metal paste to the contact surface of a second component connected to the first component;
(3) creating a sandwich structure having the two components and a layer of metal paste between them;
(4) drying the layer of the metal paste between the two components;
(5) Pressureless sintering of the sandwich structure comprising a layer of the dried metal paste,
A method of connecting components, comprising: and the drying and pressureless sintering are performed by radiation with IR radiation having a peak wavelength in the wavelength range between 750 and 1500 nm. , How to connect the components. The method of claim 1, wherein the contact surface of the component is in the range of 1 to 150 mm ² . The method of claim 1 or 2, wherein the component is selected from the group consisting of a substrate, an active component, a passive component. The metal paste applied in step (1) and optionally in step (2) comprises 25 to 90% by weight of sinterable metal particles, 5 to 30% by weight of organic solvent, 0% of metal precursor compound. 4. The method according to any one of claims 1 to 3, comprising from 0 to 65% by weight, 0 to 5% by weight of sintering aid, and 0 to 5% by weight of other additives. The method according to any one of claims 1 to 4, wherein 95 to 100% by weight of the organic solvent or organic solvents originally contained in the metal paste is removed during the step (4). The method according to any one of claims 1 to 5, wherein the peak wavelength is in a wavelength range of 750 to 1200 nm. 7. The method according to any one of claims 1 to 6, wherein the drying and pressureless sintering are in each case carried out solely by radiation with IR radiation. 8. The method according to any one of claims 1 to 7, wherein one or more NIR emitters operated at a power output in the range of 15 to 100 w/cm are used as a radiation source for IR radiation. 9. The method of claim 8, wherein the emitter surface temperature of the NIR emitter or NIR emitters is in the range of 1800-3000°C. 10. The method of any one of claims 1-9, wherein one or both of the components are transparent to the IR radiation. 11. The method of claim 10, wherein the IR radiation is from the top via the component located on the top and transparent to the IR radiation. 12. Method according to any one of the preceding claims, wherein the distance between the radiant discharge surface of the IR radiation source or radiation sources and the layer of metal paste is at a distance of 1 to 50 cm. .. 13. Steps (4) and (5) are performed under an oxygen or oxygen-free atmosphere, in both cases one or both of the components has an oxygen sensitive contact surface. The method according to any one of claims. The method according to any one of claims 1 to 13, wherein steps (4) and (5) occur immediately after each other.